The invention relates to a displacer damper for a refrigerating machine having at least one cylinder/displacer arrangement.
Refrigerating machines having a hollow, generally-cylindrical space substantially closed at least at one, working end and a displacer across the hollow space and reciprocable therealong to define a variable working space between the displacer and the substantially-closed, working end of the hollow space are known and particularly useful for producing especially-low temperatures. See, for example, U.S. Pat. No. 2,906,101.
The working space is filled with a working gas and connected into a closed, working-gas loop in such a manner relative to forced reciprocation of the displacer that the working gas experiences a thermodynamic cycle (Stirling cycle, Gifford-McMahon cycle, etc.). As a result, heat is removed from one end of the working space. With a two-stage refrigerating machine of this type using helium as the working gas, temperatures of 10.degree. K. or even lower can be produced.
The displacer can be forced to reciprocate mechanically, by a connecting rod and crank shaft; pneumatically, by enclosing the other end of the hollow space, on the opposite side of the displacer from the working end, and applying high and low driving gas pressures alternately thereto; or by other arrangements. No matter how the displacer is reciprocated, however, the reciprocation of the displacer produces a universal drawback of this type of refrigerating machine; the reciprocation of the displacer must be damped or the rhythmic vibrations resulting therefrom tolerated in the refrigerating machine and, unless extremely-costly dampers are used between the refrigerating machine and connected equipment, in the connected equipment.
Damping the reciprocation of the displacer is a particular problem with pneumatically reciprocated displacers in refrigerating machines operating on a Gifford-McMahon cycle, because the minimum working space in this cycle should be extremely small. As a result, the displacer may hit the substantially-closed, working end of the hollow space to aggrevate the vibration problem from the displacer reciprocation and generate noise which, in the long run, is disturbing.
In one attempt to solve the displacer vibration problem, German patent application DAS No. 25 16 591 discloses a refrigerating machine in which the displacer is suspended from springs on both sides. The springs and displacer form a mass/spring system which, of course, complicates achieving displacer reciprocation appropriate for the desired thermodynamic cycle. Moreover, the spiral or helical springs used require a dead space (that is, the smallest cylinder space achievable at the two end positions of the displacer) which is very large. This is a particularly-serious drawback for the working space of a refrigerating machine operating on a Gifford-Mahon cycle and may make this cycle unattainable.
In another attempt, German patent application DOS No. 33 13 506 discloses a refrigerating machine in which trapped gas is said to act as a shock absorber for the displacer. However, this requires a complicated structural design. Besides, it is still inherently afflicted with the dead-space problem.